Add a link to an article or other coverage of the mystery if you can.
Here’s one: The Max Headroom signal hijacking incident
In 1987, two individuals hijacked television signals of two TV stations at night and broadcasted creepy footage of someone wearing a Max Headloom mask and costume to viewers. They were never identified.
Probably not quite what you were expecting, but:
https://en.wikipedia.org/wiki/Fermi_paradox
The argument can be summarized like this: it seems likely that intelligent life has evolved elsewhere in the universe – the universe is a big place. It took a very long time for this evolution to occur in the only case we know of – it took us billions of years. One can reasonably assume that some supposed alien intelligent life out there will evolve more quickly, others less. Statistically, we should assume that we are most-likely about in the middle in terms of our rate of evolution – it would be unexpected for us to be the very fastest-evolving intelligent life in the universe. It takes time to travel between the stars, but as best we can tell, not very long compared to the kind of time required to evolve – once a civilization is able to do travel in space, we would expect it to spread, and do so quickly compared to the time required to evolve. So if one guesses that maybe half of alien intelligent life evolved more quickly than we did, a lot of it should have had a lot of time to spread throughout the universe by now.
But we have seen nothing that appears to be alien intelligent life on Earth or elsewhere. How can this be?
There are some proposed answers to the paradox that are a bit disturbing.
We are right about at that point in technological development ourselves. We cannot yet travel to the stars, but we can travel in space, and reaching the stars does not seem to present fundamentally unsolvable challenges. If that answer is the correct one, then we would expect such a destructive event to occur to humanity before long.
I think reading up on this has made me more appreciate the profoundness of that Arthur C. Clarke quote
The possibility of being alone is not just terrifying in and of itself. Its horror is also in mulling over why we might be alone.